Showing papers in "Journal of Animal Ecology in 1951"

The length-weight relationship and seasonal cycle in gonad weight and condition in the perch (perca fl uvia tilis)

Abstract: The present paper is an account of some of the investigations on the biology of the perch (Perca fluviatilis Linn.) in Windermere, which are being conducted in connexion with a trap-fishery experiment (Worthington, 1950). This experiment is mainly a study of populations, but it has been necessary simultaneously to investigate the general biology of the perch, particularly the growth and related aspects. The computation of a formula to express the length,weight relationship and provide a means of interconverting measurements of length and weight, revealed the relative complexity of the interrelationships of length, weight and condition. Condition in turn was found to be correlated with the seasonal changes in gonad development and growth, and the importance of the effect of stomach contents on weight had also to be assessed. It was decided, therefore, to combine these separate but interrelated aspects in one paper. The main part of the paper is devoted to the questions of length-weight relationship and condition. A brief review of the fundamental bases for the concepts of length-weight relationship and condition and of some of the methods of analysis of length-weight data precedes an account of the application of the chosen methods to the present material and its results. This is followed by an account of seasonal changes in gonad weights. A brief account is then given of the rather scanty data available on the weight of stomach contents. The seasonal changes in condition are then described and, finally, some of the results are summarized, combined and discussed as a picture of the seasonal cycle in the Windermere perch. In the statistical analysis of the length-weight relationship the data for only one group of fish are given in full (Tables i and 2) as an example of the method of computation used for all the groups. Again, in the section on seasonal changes in gonad weight and condition Figs. 2-7 are based partly on tables of data which are not published. The full tables have been deposited with the Freshwater Biological Association, from whom copies can be obtained.

Observations on the Orientation of Some Species of Barnacles

Abstract: There are in the literature a number of conflicting statements regarding the effect of various stimuli on the cypris stage of barnacle larvae, before and at the time of metamorphosis, and little experimental work has been done to elucidate the type of reactions involved. Visscher (1928), working with Balanus amphitrite, B. improvisus and Chthamalus fragilis, stated that during the earlier part of their free-swimming stage the cypris larvae were positively phototropic, but later the reaction to light became erratic, and at the time of attachment was decidedly negatively phototropic. He further stated that in a settlement experiment they orientated with the anterior end (i.e. with the paired eyes) away from the light source. However, MacDougall (I943) working with two of the above species (Balanus improvisus and Chthamalus fragilis) and also Balanus eburneus, and Pyefinch (I948) working with B. balanoides and B. crenatus, both state that the cypris larvae retain their positive reaction to light up to the time of settlement. There also appears to be some disagreement regarding the orientation at, and subsequent to, metamorphosis of several species of barnacles. Moore (1935), in considering B. balanoides, has suggested that if a barnacle is settling in a current, then at the time of settlement it is likely to be orientated with the current. A general orientation at right angles to the current was supposed to be due to rotation after settlement. This rotation was considered to be a response to the orientation of the beating cirri in relation to the current; it was suggested that feeding would be more effective with the animal orientated across the current.

The pollen collected by bumble-bees

Abstract: This study was carried out in western Scotland (Dunbartonshire) where the Bombidae, though numerous, are represented by few species. Bombus lucorum L., B. agrorum Fabricius, B. hortorum L. and B. pratorum L. are all common, the first being perhaps the most abundant. Only two other species, B. terrestris L. and B. jonellus Kirby, have been seen and these infrequently. The colonies whose pollen collection was investigated were all obtained within a radius of about a mile (National Grid reference: 26/323808). Nearly all were dug up towards the end of their season, but some that were taken early in the summer were kept in observation nests until they died out. Details of the nests are given in Table i.

The Night-Resting Habits of Monkeys in a Small Area on the Edge of the Semliki Forest, Uganda. A Study in relation to the Epidemiology of Sylvan Yellow Fever.

Abstract: During recent years much information has been gathered regarding the importance of wild animals in the epidemiology of sylvan yellow fever in Africa. That relating to the area in which the present work has been done is reported by Haddow, Smithburn, Mahaffy & Bugher (I 947) and their main findings may be summarized briefly here. Immunity to yellow fever was found to be widespread among the monkeys of the lowland Semliki forest but non-existent in any of the many other animal groups investigated. Although the several species of monkey studied had various day-time habits, some keeping purely to the trees and others spending more or less time on the ground, no significant differences in the immunity rates correlated with these particular differences were detected. It was deduced, therefore, that, if a single main vector insect were concemed, all species must be infected at a time and in a place in which they all adopt a like habit. Such a condition is fulfilled at night, as most species sleep in trees during this period. Entomological investigations in the same locality, devoting particular attention to the vertical distribution and daily rhythm of biting by forest insects

An Ecological Survey of the Cheshire Foreshore of the Dee Estuary

Abstract: i. DESCRIPTION OF THE AREA 3. . I3 (a) Historical changes caused by man . 103 (b) Other causes of change 104 (c) Conditions in 1946-7 . 105 2. FACTORS AFFECTING THE PRESENCE AND DISTRIBUTION OF SPECIES . . . . . I05 (a) Salinity . . . . . . 105 (b) Exposure . . . . . . 1O9 (c) Silt content and water content . . lO9 (d) Texture . . . . . . IO (e) Pollution . . . . . . IO 3. METHODS . . . . . . . 110

Further Observations of the Night-Resting Habits of Monkeys in a Small Area on the Edge of the Semliki Forest, Uganda.

Abstract: Lumsden (I95I) carried out a thorough study of the sleeping habits of the monkey population living at Mongiro, on the edge of the Semliki Forest, in Bwamba County, Western Uganda. He used African observers, under the charge of a reliable African supervisor, to record the trees in which inactive monkeys were seen at dusk and dawn. The trees were numbered with metal tags nailed to the trunk. The present writer visited the same area on 4, 6 and 7 July, I950, in company with the same African supervisor, and the most experienced observer. Many of the trees still bore the numbered tags. Those that had lost their tags were readily recognized by one or both of the Africans, and the identifications were checked by referring to Lumsden's map. Reference should be made to the previous paper for information on the monkeys, and a detailed description of the area. Individual trees are referred to below by the numbers used by Lumsden. The only species of monkey seen to occupy numbered trees during the 3 nights of observation were Colobus abyssinicus ituricus Matschie (Lowland colobus), Papio doguera tessellatus Elliot (Anubis baboon) and Cercocebus albigena johnstoni Lydekker (Black mangabey).

Seasonal changes in flight direction of migrant butterflies in the British Isles

Abstract: For many years naturalists were reluctant to admit that butterflies, moths and other frail insects were capable of undertaking unidirectional 'migration' flights of hundreds of miles or more. When the evidence of this became overwhelming, it was held that the flights were 'over-flow' movements from over-populated districts, and could not be compared with the 'real' migration of birds. True migration must consist of a to-and-fro movement of the population in one direction at one time of the year and in an opposite direction at a later season. In fact, in the north temperate areas, what was considered necessary to establish the existence of migration was evidence of a movement to the north in the spring and to the south in the autumn. Round about the year 1920 only one butterfly was generally admitted to be a migrant in this sense: the monarch (Danaus plexippus L.) of North America. In this insect there was considerable evidence of a southward movement in the autumn, and slight evidence of a return movement in the spring. In 1930, I published a book on the Migration of Butterflies (Williams, 1930), bringing forward evidence, of various degrees of incompleteness, for migration in over 200 species of butterflies from many parts of the world. There was also small evidence of a return flight in about half a dozen species. Even at that date, however, there were competent entomologists who would not accept the idea that such movements were anything but exceptional outflows, without any relation to regular migration of birds. Dr A. H. Clark, one of the best of the North American lepidopterists, did not even accept the reality of the migration of the monarch butterfly till about eight years later. Heape, in his book on Emigration, Migration and Nomadism, which was published posthumously in I 93 i, but actually written before my own book appeared in I 930, expressed fully the then prevailing view that 'to-and-fro' migration was fundamentally different in origin from overflow movements in one direction only, and that true migration was only known in one single species of butterfly-the monarch. In 1936, Grant brought forward evidence of a northward movement of the red admiral butterfly (Vanessa atalanta L.) in the British Isles which lasted during May, June and July, and of a southward movement in September and October. This will be referred to again later. In I942, I brought forward evidence for a return flight at a different time of the year in a dozen species of butterflies and two species of moths (see Williams, Cockbill, Gibbs & Downes, I942, pp. 240-8). The butterflies included, in addition to those mentioned above, Phoebis sennae L. in America, Catopsilia pyranthe L. in India; Colias croceus Fourc. in western Europe; Kricogonia lycide Godt. and Ascia monuste L. in southern North America and in Central America; Vanessa cardui L. in Europe; Dione vanillae L. in Florida; Libythea labdaca Westw. in West Africa; and Danaus berenice Cr. in Florida. In fact I had then come to the conclusion that evidence for a return flight is found in a species as soon as close observations are made and a sufficient number of observers are available. It appears that in many cases the flight in one direction is gregarious and in large numbers, while the flight in the opposite direction is in small numbers with the butterflies flying singly. So long as we remained dependent for information on the accidental reports of field naturalists, the evidence was biased in favour of the conspicuous flights in one direction; when more careful observations were made the second movement began to be noticed. Shortly after the publication of my book in 1930, an organization was formed in south-eastern England, largely by the energy and enthusiasm of Captain T. Dannreuther, to watch for evidence of directional movements of butterflies and other insects in the British Isles; and also to collect records of the occurrence of known immigrants in Britain even if there was no immediate evidence of directional movements. This organization is known as the 'Insect Immigration Committee of the SouthEastern Union of Scientific Societies'. Hundreds of

A Note on the Papers of Elton and Williams on the Generic Relations of Species in Small Ecological Communities

Abstract: The Easter Symposium of the British Ecological Society on 'The Ecology of closely allied species' (Anon. I944) considered Gause's contention (I934) that two species with similar ecology cannot live together in the same place. Elton published his contribution to this meeting in an expanded form (Elton, I946), giving an analysis of 55 animal and 27 plant communities, and calculating the number of species per genus for each community, the average of which was found to be i 38 for animal, and I'22 for plant communities. Elton also considered the number of species per genus in faunal lists, taking A check list of British insects (Kloet & Hinks, I945) as an example. In this case he calculated the number of species per genus to be 4-23. He attributed (p. 66) 'the differnce in species/genus frequencies between ecological surveys of relatively small parts of any general habitat, and those for faunal lists from larger regions,. .. to existing or historical effects of competition between species of the same genus, resulting in a strong tendency for the species of any genus to be distributed as ecotypes in different habitats, or if not, to be unable to co-exist permanently on the same area of the same habitat.' This paper was criticized by Williams (I 947) who, using a statistical method based on the logarithmic series, re-analysed 13 of Elton's communities and showed that they contain fewer genera than would be expected in a sample of the same number of species taken at random (i.e. independent of generic relations) from a suitable fauna or flora list. This, he concluded (p. I7), 'can only be interpreted as a natural selection-in the course of time-in favour of species in the same genus rather than against them. It is possible to suggest reasons for this-for example, if one species in a genus is capable of survival in a given physical environment, it seems likely that other species in the same genus might be more likely to have a similar genetic make-up than species in another genus, and so might have a good chance of survival' Before attempting some closely related work, it was found necessary to attempt a reconciliation between these two conflicting views, and the present note is the result of a consideration of the thirteen communities used by both Elton and Williams from the point of view of their suitability for the type of analysis to which they have been subjected; from this consideration three important points have emerged. First, the habitats of many of the communities are very heterogeneous, in some cases including species from several totally dissimilar minor habitats. For example, the list analysed as community 20 (community numbers refer to Table I, p. 55 of Elton, I946) was compiled from samples taken from five stations chosen over a 5o-mile stretch of the River Wharfe (Percival & Whitehead, I930). The distances between adjacent stations varied from 6 to 26 miles; and from the first station at Grassington to the last at Ullskelf the river changes from a fastflowing mountain river with a rocky bottom, to a placid alluvial lowland river. The list on which community i 2 was based was derived from a survey by Pyefinch (I937) of eight pools on Bardsey Island, ranging from brackish to fresh-water conditions. Pyefinch stresses (p. I37) 'the great variation in the environment from one pond to another, as each is influenced to a considerable extent by purely local conditions'. Indeed he states (p. I I7) that the ponds were 'so chosen that the full range of environment was adequately represented'. Similar criticisms apply to community I3 (Laurie, I942) and also to community 14 (Humphries, 1936) where, in the original survey, particular attention was paid to two stations as they represented physiographically different habitats. In these cases Elton and Williams have considered the occupants of a variety of habitats as constituting one community, even when the authors of the original papers have gone out of their way to stress that the sampling stations were chosen expressly because of their dissimilarity. Both authors were interested in animals living together in one habitat in competition with each other, so that the choice of many of the communities, especially the Bardsey Ponds with their great physical and chemical differences making them quite unsuitable for the type of analysis to which they were subjected, was particularly unfortunate. Secondly, it should be noted that the animals in the original lists were often collected by means of a variety of sampling devices. For example, the

The Dispersal of Urceolaria mitra (Peritricha) Epizoic on Flatworms

Abstract: Urceolaria mitra Von Sieb belongs to the peritrich family of Protozoa, the Urceolaridae, and according to Hirshfield (I 949) eleven species have been recorded, all from invertebrates. Nine occur on marine hosts, one on a land-snail, while U. mitra is the only freshwater species. Some of the Urceolarids, particularly those belonging to the genus Trichodina, are definitive parasites of fish, while others such as Urceolaria mitra are better referred to as epizoic for the time being. The latter is found on the surface of flatworms and occurs most abundantly on the triclad Polycelis tenuis Ijima (Reynoldson, I947, 1948). These peritrichs move freely about the dorsal surface and when stimulated, for example by light, become very active. A series of typical shapes is shown in Reynoldson, (I950, Fig. I). A preliminary account of its seasonal population fluctuations has been given already (Reynoldson, I950) together with the references to the biology of these organisms. The small, ornamental pond in the grounds of the Memorial Buildings, Bangor, where the observations on dispersal were made, was also described in that paper. The early population work on Urceolaria mitra, done outside the breeding season of the flatworm and when the peritrich population was high, showed every specimen of Polycelis tenuis to be infested. But this incidence was reduced later because young worms were often without the epizoite. It also declined during periods of population depression of the peritrich when worms of all sizes were found free. These points receive attention in the paper already referred to, but the problem of dispersal vital to an understanding of population fluctuations is examined in PAGE 5. AN ANALYSIS OF DISPERSAL METHODS . 26 6. THE NATURAL INFESTATION OF FLATWORMS AND THE BUILDING UP OF THE URCEOLARIAN POPULATION . . . . . . 128 7. DISCUSSION . . . . . . . I29 8. ACKNOWLEDGEMENTS . . . . . 130 9. SUMMARY . . . . . . . 130 REFERENCES . . . . . . . 130

The Population of Rooks (Corvus frugilegus) in West Gloucestershire. II

Abstract: I936 fall is therefore probably not significant, that of I938 may be. An attempt has been made to relate this fall to other factors. The numbers of nests have been compared with the Ministry of Agriculture and Fisheries' returns for 4 June of the previous year, proportionate adjustments being made to allow -for the fact that the area under survey does not exactly follow the parish boundaries. One anomaly was immediately apparent; between 4 June I932 and 4 June I933 the total area of agricultural land (crops and grass) fell by about I7%; it remained sensibly constant until I936, and then in I937 rose to about its I932 value, where it remained. This cannot mean that there was any real change of land use, but must indicate some changing method of filling up the Ministry's forms. No figures are therefore given for this factor. Acreage of cereals, of cereals; roots and potatoes; and of total arable land varied irregularly from year to year, though the three factors generally moved in the same direction. There is, in general, no connexion between the movements in the acreage of arable and the rook population, but the years I936 and I937 are I35 % and 8-8% respectively below the average in acreage of cereals. It is possible that this was a partial cause of the fall in population in I938. The cereal acreage in I938 was a little above average. Further reference to this point is made below. During the war of I939-45 there was much ploughing of grassland, and in I943 the acreage of cereals was about seven times, and that of total arable about five times, those of the years I933-8. The significant, but not large, increase in the number

The Effect of Vegetation on the Breeding of Newts, Molge cristata and Molge vulgaris

Abstract: According to Stolte (192ia, b), in some aquatic oligochaetes (Naiads) sexual reproduction is governed by the oxygen given off by algae. Here there is an optimum, deficiency or superfluity of oxygen being unfavourable. Miyazaki (1938), dealing with oysters, has reported a substance contained in green algae which produces spawning in the male oyster. In the observed breeding -habits of fishes, there is frequent reference to association with aquatic vegetation. Among the fresh-water fishes for instance, sticklebacks, the bowfin (Boulenger, I93i) and the gourami (cited by Meek, I9I6) are known to make nests among water plants, while the common carp, Cyprinus carpio (Boulenger, 193I) and the European catfish, Silurus glanis (Meek, I 9 I 6), both deposit eggs on water plants. Among marine fishes wrasses and the Saragossa fish (Boulenger, 193I) nest among seaweed and the eggs of skates and rays are anchored among weeds. To these instances of the association of a special type of environment with the reproduction of aquatic animals I must add a casual observation of my own on a fresh-water vertebrate. I noticed, one spring, that common newts kept for some days in a gold-fish bowl with clean water and no weed made no attempt to spawn, but proceeded to deposit ova almost immediately after the introduction of the pond-weed Elodea canadensis. During the course of experiments shortly to be described and which are prompted by this casual observation, Dr Harding of the British Museum informed me that he had had a similar experience with Amblystoma. I quote from his letter with his permission. 'The female had been in the water for some months.... There was no weed in the pond. On the I2th of last month (June 1938) a lab. boy brought me some weed which I had placed in the water and on the I3th there were eggs! The male was still on land, but one presumes that, either he went in the water for a time or the female came out for him.' Finally, long after the completion of the investigations dealt with in this paper, there came to my notice an account by Van Nieuwenhoven & Lever (1946) of similar work carried out in Holland during the war. The Dutch workers found snails of the genus Limnaea kept in aquaria without water plants and fed regularly on lettuce reacted to the addition of water plants by producing eggs within a few hours. In the account that follows I give the results of experiments designed to test the importance of vegetation and associated factors on the reproduction of newts. These experiments were carried out in I936 and 1938 at Roman Hill Boys' School, Lowestoft, and they were only made possible by the help and close co-operation of the Headmaster, Mr W. H. Bleby, and two members of his staff, Mr Railston, in I936 and Mr Bentley in 1938. In addition, I include some experiments on a smaller scale which I made in 1937. I have also to thank Dr E. S. Russell, Dr J. P. Harding, and Dr C. F. A. Pantin for reading through the paper and for helpful suggestions in interpreting the results.